Sensor

Abstract

The probability of a heater portion of a sensor element being exposed to water is lowered. The sensor element includes a built-in heater that extends in a longitudinal direction and a surrounding housing extending in the longitudinal direction. The heater includes a heat generation portion and a lead portion. The heat generation portion has a front end and a rear end, and is positioned on the same side as a front end portion side of the sensor element. The housing includes an enlarged diameter portion having a diameter of an inner wall that increases in a direction toward the front end of the sensor. The enlarged diameter portion includes a front end portion and a rear end portion. The rear end of the heat generation portion is located closer to the front end of the sensor than the rear end portion of the enlarged diameter portion is.

What is claimed is: 
     
       1. A sensor comprising:
 a sensor element that includes a built-in heater and extends in a longitudinal direction; and 
 a housing that is formed so as to extend in the longitudinal direction and surround the sensor element, 
 wherein the sensor element includes a front end portion and a rear end portion, 
 the heater includes a heat generation portion and a lead portion, 
 the heat generation portion has a front end and a rear end, and is positioned on the same side as the front end portion side of the sensor element, 
 the housing includes an enlarged diameter portion that is formed so that a diameter of an inner wall of the housing increases in a direction toward the front end of the sensor, in a cross section that is parallel to an axis that extends in the longitudinal direction, 
 the enlarged diameter portion includes a front end portion and a rear end portion, and 
 the rear end of the heat generation portion is located closer to the front end of the sensor than the rear end portion of the enlarged diameter portion is. 
 
     
     
       2. The sensor according to  claim 1 ,
 where the enlarged diameter portion is formed so as to have a shape with a taper in the cross section. 
 
     
     
       3. The sensor according to  claim 2 ,
 wherein the angle of the taper is no less than 10 degrees and less than 90 degrees. 
 
     
     
       4. The sensor according to  claim 2 ,
 wherein the angle of the taper is no less than 20 degrees and less than 90 degrees. 
 
     
     
       5. The sensor according to  claim 2 ,
 wherein the angle of the taper is no less than 30 degrees and less than 90 degrees. 
 
     
     
       6. The sensor according to  claim 1 ,
 where the enlarged diameter portion is formed so as to have a rounded shape in the cross section. 
 
     
     
       7. The sensor according to  claim 1 , further comprising
 a protective cover that extends in the longitudinal direction and surrounds at least a portion of the enlarged diameter portion of the housing, and is formed so as to extend beyond the front end portion of the sensor element. 
 
     
     
       8. The sensor according to  claim 1 ,
 wherein the sensor element has a porous protective layer that covers at least a portion of the sensor element. 
 
     
     
       9. The sensor according to  claim 1 ,
 wherein the sensor element is a gas sensor element.